Patch a list of Lists into L. Patches from left to right, first items get completed by the next ones (last-in completes).
L
to start with
(?='flat') 'deep' to do it deeply
'flat'
(?=BuiltIn) types not to merge
BuiltIn
(?=never) types of O to be replaced with ones of O1
never
O
O1
to patch
List
Patch a list of Lists into
L. Patches from left to right, first items get completed by the next ones (last-in completes).